class Solution {
    public String longestCommonPrefix(String[] strs) {
        if(strs == null || strs.length == 0) {
            return "";
        }
        String ss = strs[0];
        for(int i = 1;i < strs.length;i++) {
            ss = ifCommon(ss,strs[i]);
            if(ss.length() == 0) {
                break;
            }
        }
        return ss;
    }

    public String ifCommon(String str1,String str2) {
        int length = Math.min(str1.length(),str2.length());
        int index = 0;
        while(index < length && str1.charAt(index) == str2.charAt(index)) {
            index++;
        }
        return str1.substring(0,index);
    }
}